介绍

Bootstrap是一个流行的前端框架，它提供了许多有用的特性，包括灵活的响应式网格系统、强大的样式组件和易于使用的插件等等。其中一个重要的插件就是图片轮播组件，这个组件可以用来创建各种各样的漂亮的轮播效果，这篇文章将详细讲解多种Bootstrap图片轮播效果的实现。

准备工作

在开始编写Bootstrap图片轮播之前，需要先引入jQuery和Bootstrap的CSS和JS文件。

<!doctype html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Bootstrap 图片轮播效果</title>
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.1/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
</head>
<body>
  ...
</body>
</html>

实现

基础轮播

一个基本的轮播需要三部分内容：

用 <div> 标签包围一个图片列表
给包围图片列表的 <div> 标签添加 carousel 和 slide 两个类（slide 标识是轮播内容是滑动还是淡入淡出）
添加用于控制轮播的箭头和指示符

<div id="carouselExampleSlidesOnly" class="carousel slide" data-ride="carousel">
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="img/slide-1.jpg" alt="First slide">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-2.jpg" alt="Second slide">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-3.jpg" alt="Third slide">
    </div>
  </div>
</div>

为了实现箭头的控制，在图片轮播 <div> 内需要添加一个包含类名为 carousel-control-prev 的 <a> 标签和一个包含类名为 carousel-control-next 的<a> 标签。在每个 <a> 标签内添加一个小图标样式即可。

<div id="carouselExampleSlidesOnly" class="carousel slide" data-ride="carousel">
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="img/slide-1.jpg" alt="First slide">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-2.jpg" alt="Second slide">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-3.jpg" alt="Third slide">
    </div>
  </div>
  <a class="carousel-control-prev" href="#carouselExampleSlidesOnly" role="button" data-slide="prev">
    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
    <span class="sr-only">Previous</span>
  </a>
  <a class="carousel-control-next" href="#carouselExampleSlidesOnly" role="button" data-slide="next">
    <span class="carousel-control-next-icon" aria-hidden="true"></span>
    <span class="sr-only">Next</span>
  </a>
</div>

多种效果轮播

淡入淡出

淡入淡出的标志是轮播内容的过渡方式采用了淡入淡出的方式，这也使得轮播更加优雅。

<div id="carouselExampleFade" class="carousel slide carousel-fade" data-ride="carousel">
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="img/slide-1.jpg" alt="Slide 1">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-2.jpg" alt="Slide 2">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-3.jpg" alt="Slide 3">
    </div>
  </div>
  <a class="carousel-control-prev" href="#carouselExampleFade" role="button" data-slide="prev">
    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
    <span class="sr-only">Previous</span>
  </a>
  <a class="carousel-control-next" href="#carouselExampleFade" role="button" data-slide="next">
    <span class="carousel-control-next-icon" aria-hidden="true"></span>
    <span class="sr-only">Next</span>
  </a>
</div>

带缩略图

有时候，我们需要一个轮播效果，能够加入缩略图来展示图片的预览。Bootstrap提供了 carousel-indicators 类，以实现一个缩略图导航指示器。

<div id="carouselExampleIndicators" class="carousel slide" data-ride="carousel">
  <ol class="carousel-indicators">
    <li data-target="#carouselExampleIndicators" data-slide-to="0" class="active"></li>
    <li data-target="#carouselExampleIndicators" data-slide-to="1"></li>
    <li data-target="#carouselExampleIndicators" data-slide-to="2"></li>
  </ol>
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="img/slide-1.jpg" alt="Slide 1">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-2.jpg" alt="Slide 2">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-3.jpg" alt="Slide 3">
    </div>
  </div>
  <a class="carousel-control-prev" href="#carouselExampleIndicators" role="button" data-slide="prev">
    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
    <span class="sr-only">Previous</span>
  </a>
  <a class="carousel-control-next" href="#carouselExampleIndicators" role="button" data-slide="next">
    <span class="carousel-control-next-icon" aria-hidden="true"></span>
    <span class="sr-only">Next</span>
  </a>
</div>

带标题和描述

有时候，轮播图不仅需要通过图片展现内容，还需要通过标题和描述说明和点出重点。Bootstrap提供了添加标题和描述的方式，需要在依次添加 HTML 的代码块，并修改 .carousel-caption 样式来实现。

<div id="carouselExampleCaption" class="carousel slide" data-ride="carousel">
  <ol class="carousel-indicators">
    <li data-target="#carouselExampleCaption" data-slide-to="0" class="active"></li>
    <li data-target="#carouselExampleCaption" data-slide-to="1"></li>
    <li data-target="#carouselExampleCaption" data-slide-to="2"></li>
  </ol>
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="img/slide-1.jpg" alt="First slide">
      <div class="carousel-caption d-none d-md-block">
        <h3>First slide label</h3>
        <p>Nulla vitae elit libero, a pharetra augue mollis interdum.</p>
      </div>
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-2.jpg" alt="Second slide">
      <div class="carousel-caption d-none d-md-block">
        <h3>Second slide label</h3>
        <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
      </div>
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="img/slide-3.jpg" alt="Third slide">
      <div class="carousel-caption d-none d-md-block">
        <h3>Third slide label</h3>
        <p>Praesent commodo cursus magna, vel scelerisque nisl consectetur.</p>
      </div>
    </div>
  </div>
  <a class="carousel-control-prev" href="#carouselExampleCaption" role="button" data-slide="prev">
    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
    <span class="sr-only">Previous</span>
  </a>
  <a class="carousel-control-next" href="#carouselExampleCaption" role="button" data-slide="next">
    <span class="carousel-control-next-icon" aria-hidden="true"></span>
    <span class="sr-only">Next</span>
  </a>
</div>